1. Field of the Invention
The present invention relates generally to nonintrusive arrangements for determining the direction of a neutral particle beam, particularly by measurement of residual charged particles having the same directional characteristics as neutral particles making up the neutral particle beam.
2. Description of the Prior Art
Various areas of technology today employ neutral particle beams. In addition to civilian uses such as heating of fusion plasmas and medical research, neutral beams have military importance as potential weapons used both in the earth's atmosphere and out in space. Any of the practical uses of neutral beams require an ability to direct the beam in a controlled manner. A fundamental aspect of such beam control is determining the direction of a neutral beam at any point in time. A problem here is in determining the direction of neutral particles without interrupting the beam. It is also difficult to detect and measure neutral particles.
Four approaches have been proposed for determining the direction of neutral particle beams. The first is a resonant Doppler-shift laser system which is costly and difficult to operate, requiring highly skilled personnel operating in a highly controlled environment. The second technique, commonly known as the "pinhole" technique, measures the direction of beam samples taken from the periphery of a neutral particle beam. In this second technique, the interior of the beam cross section is not analyzed. This is a significant drawback since neutral beams for several important potential applications may be non-uniform in their cross-sectional and directional properties.
The third technique utilizes laser-induced fluorescence to excite some of the atoms in the beam which are in excited states to higher states. These highly excited beam atoms radiate a short time later, and the angle of interception between the laser beam and the neutral beam which gives the maximum intensity of fluorescence yields a measure of the direction of the neutral beam. This technique suffers from the same problems as the first method. The fourth technique, "wire shadows," employs two wires which intercept the neutral beam. One wire is downstream to the second, and they are in close proximity to each other. The current in the second wire due to the impact of the neutral beam is a measure of the direction of the neutral beam. Difficulties have been encountered in aligning these wires with respect to one another. This alignment problem is further exacerbated by space qualification requirements.